Methyl vinyl ketone terpolymers



Aug. 28, 1962 R. J. sLocoMBE ETAL 3,051,685

METHYL VINYL KETONE TERPOLYMERS Original Filed Dec. 7; 1955 2Sheets-Sheet 1 AvxwAvAvA `NAmm?,SEMA AvAvAyximAvA AvAvAvAvmvAAyAAvAvAvAv ,vmmm AvAyAvAvA AvAvAYm AVA ae V VAVAVA AVAVAVAv AvAvAvAAVAVAVAVA VAVAVAVAVA AVAVAVAV# %VAVAVAVA VA WAVAVA AVAVAV# I AVAV AVAVAAVAVA VAYA AV .A AVAVAVAV VAVAVAVA VA AVAVAVAVAVA AVAVAVAVAVAVVVVVVVVVVVVVVV ACRYLONITRILE METHYL FUMARATE me. 1 STYRENC-/ACQYLOm-rme/mETHYL FUMAQATE TERPOLYMERS RoERT J. SLocoME GEORGE 1 WaSP INVENTORSATTORNEY Aug. 28, 1962 R. .1. sLocoMBE ErAL 3,051,585

METHYL VINYL xEToNE TERPOLYMERS Original Filed Dec. 7, 1953 2Sheets-Sheet 2 AVAVA AVAVAVAY VV V ROERT J. SLocomE GEGRGYE L, was? INVENTOR.

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ATroRNEY Uite 3,351,685 PatentedrAug. 28, 1962 3,6SL685 lVlETHYL VNYLKETNE TERPOLYNEERS Robert J. Slocombe, Dayton, and George L. Wesp,Englewood, Ohio, assignors to Monsanto Chemicai Cornpany, St. Louis,Mo., a corporation of Delaware Original application Dec. 7, 1953, Ser.No. 396,506, now

Patent No. 2,829,128, dated Apr. 1, 1958. Divided and this applicationMar. 3i, 1958, Ser. No. 725,030

6 Claims. (Cl. 2613-63) This invention relates to three-componentinterpolymers, commonly called terpolymers, i.e., interpolymers preparedby polymerizing a monomeric mixture consisting of three differentmonomers. In specitic aspects the invention pertains to terpolymers of(a) a monomer selected from the group consisting of styrene,vinyltoluene, and vinylxylene, (b) acrylonitrile, and (c) a monomerselected from the group consisting of dialkyl fumar-ate, methacrylicacid, methacrylonitrile, alkyl methacrylate, methyl vinyl ketone,monoalkyl fumarate, and monoalkyl maleate. ther aspects of the inventionrelate to improved methods of preparing clear terpolymers.

This application is a `division `of our copending application Serial No.396,506, iiled December 7, 1953, issued as U.S. Patent 2,829,128 onApril 1, 1958. Said U.S. 2,829,128 claims certain terpolymers of (a) amonomer selected from the group consisting of styrene, vinyltoluene andVinylxylene, (b) acrylonitrile, and (c) a dialkyl fumarate, andprocesses for making same, whereas the present application claimscertain terpolymers of (a) a monomer selected -from the group consistingof styrene, vinyltoluene and vinylxylene, (b) acrylonitrile, Iand (c)methyl vinyl ketone, and processes for making same.

It is by now well known that ethylenically unsaturated monomers differgreatly in their polymerization reactivity toward each other. There arein yfact some monomers that will not undergo homopolymerization at all,i.e., polymerization of two or more molecules of the same monomer toform a polymer of that monomer, yet will readily undergointerpolymerization with certain other monomers. Inter-polymerizationadords a method of imparting varying characteristics to la polymer, andin many instances such characteristics cannot -be obtained by merephysical adrnixture of two or more homopolymers. However, because of theabove-mentioned differences in reactivity among monomers toward eachother, marked heterogeneity is the rule in interpolymers and only underspecial circumstances can an interpolymer be obtained that is ofsuicient homogeneity to give a transparent or clear nterpolymer. Whilesome objectionable properties such as color, encountered ininterpolymers, can often be avoided by means such as the use ofstabilizers or lower polymerization temperatures, incompatibilitymanifested by haze, turbidity, or opacity in plastics is not overcomerby such treatment.

If a monomeric mixture is subjected to polymerization and the initialincrement of polymer is segregated before the polymerization is allowedto go forward to an appreciable extent, it .is frequently possible toobtain a clear interpolymer, but the commercial impracticability of sucha procedure is apparent. On the other hand, if polymerization ispermitted to proceed to a considerable and especially to a high degreeof conversion, the more reactive monomer enters into the polymer to agreater extent than a less reactive monomer or monomers with theconsequence that residual unreacted monomer becomes more and moredepleted in the more reactive monomer, while the polymer being formed inthe latter stages of polymerization is deiicient in the more reactivemonomer. There results a polymeric material which is made up of avariety of polymer molecules running a gamut of compositions such thatthe total polymer is heterogeneous with resultant opacity and oftengreatly impaired physical properties. This phenomenon, resulting in anundesirable product, can be overcome to an appreciable but limitedextent by gradually -adding during the course of the polymerization themore reactive monomer at a rate aimed at keeping `the composition ofunreacted monomeric mixture esentially constant. As a practical matterit is extremely difficult to approach uniformi-ty in such an operation,and it is impossible -to use this technique at all in lthe case of mass(bulk) polymerization in which the polymerization reaction mixture setsup into sem-i-solid or solid polymer after the reaction is only partlycompleted so that further access of added monomer to the total mixturecannot be obtained.

It is only in recent years that systematic laboratory and theoreticalstudies of interpolymerization have gone forward suiiiciently to permita certain amount of predictability in this eld. It has been theorizedthat in a simple binary system involving the free-radical-initiatedpolymerization of only two monomers, the composition of polymer will bedependent only upon the rate of four prop- `agation steps, i.e., stepsin ythe propagation of polymer molecules. Thus, taking a systeminvolving ltwo monomers, M1 and M2, a growing polymer chain can haveonly two kinds of active terminal groups, i.e., a group derived from M1or a group derived from M2. Either of these groups has the possibilityof reacting with either M1 or with M2. Using m1- and m2- to indicatethese active terminal groups, the four possible reactions are lasfollows:

Growing Adding Reaction chain mono- Rate of progress product mer Nwmx-Mi kulmi-lMll MNmiflLi' Nwm1- M2 k1'2[77l1- [MZl NW mimi' MN ma M2kzzlmrlMz] Nwrmzmr Nw m2' M1 kzdmz- [lVi] NW mimi' Theoreticalconsiderations lead to the now generally accepted copolymer compositionequation which describes the ratio [Mal of the molar concentrations oftwo monomers in the initial copolymer formed from a given mixture 'ofthe monomers as follows:

In this equation r1 equalsl kn/klz and r2 equals k22/k21. The terms r1and r2 :are called reactivity ratios. A very considerable body ofexperimental work has in general confirmed the copolymer compositionequation.

A large proportion of possible pairs of monomers are incapable, becauseof their respective reactivity ratios, of forming under any conditionsan instantaneous polymer rhaving the same composition as the monomericmixture from which it is formed. However there are certain monomer pairswhich, in a proportion characteristic of that pair, give a copolymerhaving the same composition as the particular monomeric mixture. In suchinstances, a batch polymerization can be carried out with a monomericmixture of the particular composition with a resultant homogeneouscopolymer containing the same relative proportions of the monomers as inthe initial monomeric reaction mixture. This composition is known of themonomers in the mixture.

' 3 as the polymerization azeotrope composition, and is represented bythe equation:

lMzl=Ti1 [M1] Tz-l Y vSuch an azeotrope composition can exist only forthose monomer pairs wherein both r1 and r2 are less than one, ortheoretically wherein both r1 and r2 are greater than one although noexamples of the latter combination are known.

While an understanding of interpolymerization involving only twomonomers is now possible to a considerable extent, because of thedevelopment of the above-discussed theories, an increase in the numberof monomers to three or more obviously tremendously increases thepossibilities and complications. Thus, for example if interpolymers of100 monomers are to be considered, there are about 5000 possible monomerpairs, but about 160,000 different combinations of three monomers arepossible, and

for each of these 160,000 combinations the variations in relativeproportions of the three monomers are ininite.

VIf the assumptions made in the development of the copoly- `mercomposition equation still hold true where three monomers are to beinterpolymerized, it is apparent that rthe composition of theterpolymers formed at any given instance will now be dependent upon therate of nine propagation steps which are dependent upon the relativeconcentrations of the monomers in the monomeric mixture and thereactivity ratio between each of the pairs j It has been pointed outthat the study of terpolymers can be simpliied somewhat by applicationof the copolymer composition equation, suitably modified forthree-component systems, so as to eliminate from consideration monomerswhose abil- 'ity to interpolymerize is so slight that further investiga--very desirable property of clarity. These terpolymers lare made bypolymerizing a monomeric mixture of certain proportions of threemonomers. The proportions giving clear terpolymers will vary from onemonomeric mixture to another depending'upon the particular monomerspresent in that mixture. The invention is particlllarly applied tomonomeric mixtures consisting essentiallyA of (a) a monomer selectedfrom the group consisting of styrene, vinyltoluene, and vinylxylene, (b)acrylonitrile, and (c) a monomer selected from the group consisting ofdialkyl umarate, methacrylic acid, methacrylonitrile, alkylmethacrylate, methyl vinyl ketone, monoalkyl fumarate, and monoalkylmaleate. For example, a monomeric mixture consisting of styrene,acrylonitrile and methyl methacrylate will, when subjected tofree-radical-nitiated batch polymerization, give a clear terpolymer onlyif the relative proportions of styrene,

racrylonitrile and methyl methacrylate are properly chosen in a mannerto be hereinafter described. In contrast, a monomeric mixture consistingof styrene, acrylonitrile and methacrylonitrile will give a clearterpolymer on being subjected to free-radical-initiated batchpolymerization only if the relative proportions of the three mentionedmonomers in the monomeric mixture are within certain limits which. ingeneral are different from those of the aforementioned mixtures ofstyrene, acrylonitrile and methyl methacrylate, and yet which are chosenin accordance with the same principle now to be discussed.

We have found that clear terpolymers of the nature described are madeprovided the proportions of three monomers in the monomeric mixture arechosen from the area lying along the line joining the binarypolymerization azeotrope composition of the particular (a) andacrylonitrile on the one hand, and the binary polymerization azeotropecomposition of the particular (a) and the particular (c) on the otherhand, as plotted on a triangular coordinate graph. By way of example,taking the case where (a) is styrene and (c) is methyl methacrylate, thepoint of the binary azeotrope composition of styrene and acrylonitrileis placed along one side of a .triangular coordinate graph at the properlocation between the apex designating percent styrene and the apexdesignating 100 percent acrylonitrile. This point is 76 to 77 weightpercent styrene and 24 to 23 weight percent acrylonitrile. On theopposite side of the equilateral triangle, constituting the triangularcoordinate graph, is Iplaced the point representing the binary azeotropecomposition of styrene and methyl methacrylate, this of course beinglocated at the proper position on the side of the triangle between theapex representing 100 percent styrene and the apex representing 100percent methyl methacrylate. This point is 54 weight percent styrene and46 weight percent methyl methacrylate. Now a straight line is drawnbetween these two points This line cuts across the triangular coordinategraph, without touching the side of the triangle opposite the styreneapex which side represents varying proportions of acrylonitrile andmethyl methacrylate in binary mixtures of same. Acrylonitrile and methylmethacrylate do not form a binary azeotrope. The said straight linejoining the two points of binary azeotrope compositions describesthree-component monomeric mixtures which, when subjected tofree-radical-initiated batch polymerization, give clear terpolymers.kFurther, there is an appreciable area lying on each side of said line inwhich the terpolymers are essentially clear. However, one cannot go toofar from this line without producing terpolymers which are not clear butrange from hazy to opaque materials. The invention particularly appliesto the area lying within 5 percent on each side of said line; said 5percent is measured on the graph in a direction normal to the line, andis equal to tive one-hundredths of the shortest distance between an apexand the side of the triangle opposite that apex. Terpolymers made bypolymerizing a monomeric mixture having a composition lying in the areaWithin 5 percent on each side of the line joining the two binarypolymerization azeotrope compositions, are generally clearer thanpolymers made from similar monomeric mixtures lying farther away fromand on the same side of the line. In most systems all terpolymers madefrom monomeric mixtures having compositions in the area lying within 5percent on each side of the line are clear. In some systems the area ofclarity may not extend as far as 5 percent from th line. Those skilledin the art, having had the benefit of the present disclosure, can easilydetermine by simple tests of the nature described herein which monomericmixtures give clear terpolymers in a given polymerization system. In allevents, the compositions of monomeric mixtures giving clear terpolymerswill be found to constitute an area lying along the line joining the twobinary polymerization azeotrope compositions.

The reasons for the clarity of terpolymers made as described are notknown. The line joining the two binary azeotrope compositions does notrepresent what might be called a series of three-component azeotropes.From much detailed data which we have obtained, the relative proportionsof the three monomers in terpolymers made from monomeric mixtures lyingalong said line are not identical to the monomeric mixture from whichthe ter-polymer is -being prepared. In other words, during the course ofa batch polymerization of a monomeric mixture whose composition is takenfrom the line,

the composition of residual monomeric material drifts and theterpolymers so formed are not homogeneous mixtures of polymer moleLulesall of which contain monomer units in the same ratio, but rather aremixtures of polymer molecules having varying proportions of the threemonomer units therein. No heretofore known scientific facts or theoriesof interpolymerization explain our discovery. However, regardless of thevarious reasons for believing that terpolymers made from compositionslying along the line as aforesaid would be heterogeneous, and regardlessof the actual reasons for the clarity of such ter-polymers, it isapparent that the present invention makes possible the production ofclear terpolymers with obvious attendant advantages, especially in lilmsand molded articles made from the terpolymers.

The accompanying drawings are triangular coordinate graphs showingcompositions O-f some three-component monomeric mixtures that give clearterpolymers on being vsubjected to free-radical-initiated batchpolymerization.

FIGURE l represents the system styrene/acrylonitrile/ diethyl fumarate.

FIGURE Il represents the system styrene/ acrylonitrile/ methyl vinylketone.

By the present invention we can subject a given monomeric mixtureconsisting of three monomers, selected as described herein, to a batchpolymerization and carry the polymerization reaction to complete oressentially complete, say 90 to 100 percent, conversion of `all of themonomers and yet obtain a clear solid resinous terpolymer. If desired,the polymerization can be stopped at anypoint short of completion solong as polymerization conditions are such as to produce solidterpolymer, but this is not necessary in order to obtain a clearterpolymer and would seldom be advantageous. The higher the degree ofconversion of monomeric mixtures, the greater the advantages of ourinvention. This is because the greatest extent of heterogeneity islfound with complete conversion to polymers. A high conversion, i.e., atleast 50 weight percent conversion and preferably at least 8O weightpercent conversion, is preferred in practicing the invention. However,some of the benefits of the invention may be realized even where thepercentage conversion is as low as percent. With very low conversions,the polymer formed tends to approach the perfect homogeneity existing inthe rst inlinitely small increment of polymer formed. As pointed outabove, commercial practicality requires that conversion be carried to avalue more than a few percent, hence introducing the lack of homogeneitywhich up to now, the art has not known how to avoid other than bytechniques such as gradual monomer addition. It is to be recognized thatthe extent of the area of clear terpolymers, lying along the linejoining the two binary polymerization azeotrope compositions, isdependent not only on the particular polymerization system but also onthe percentage conversion, said area being the greater the lower thepercentage conversion, and the smaller the higher the percentageconversion. It is observed that the terpolymers become clearer as the4composition of the monomeric mixture approaches the line joining thetwo binary azeotrope compositions, the general rule being that theclearest terpolymers are those derived from monomeric compositions lyingon the line.

lt is usually desirable that the three-component monomeric mixturecontain at least 2 weight percent, and preferably at least 5 weightpercent, of the monomer present in the smallest amount.

The invention is broadly applicable to any free-radicalinitiatedinterpolymerization of three-component monomeric mixtures containing themonomer combinations and in the proportions set forth herein, providedthe polymerization is carried out by a batch procedure. By this it ismeant that all of the monomeric materials to be employed are introducedsimultaneously in the `desired proportions into the polymerizationreaction system. Ordinarily a single charge of monomeric materials willbe placed in a reaction vessel and the single charge subjected topolymerization conditions until the polymerization is substantiallycomplete. However, it is not outside the scope of our invention tolintroduce continuously a monomeric mixture containing t-he threemonomers in iixed proportions into a dow-type polymerization system,whereby the initial polymerizable mixture passes away from its point ofintroductionand ultimately is recovered as polymer. This can beaccomplished by continuous owing of the monomeric mixture into the irstof a series of polymerization reaction vessels with continuous ilow ofreaction mixture from one vessel to another along a series of two ormore such vessels with ultimate recovery of polymer from the last in theseries. Those skilled in the art will understand that this operation isessentially a batch operation in the sense that additional monomericmaterial of composition different from the original mixture is notintroduced into a partially polymerized material. Thus, the term batchpolymerization, as used herein, means a `polymerization which does notinvolve the gradual or incremental or subsequent addition of va .monomeror monomers having a composition different from the Vinitial monomericmixture.

The invention is perhaps `most advantageously eifected by the .mass orbulk polymerization procedure. In such procedure the vreaction mixtureis free from added solvent or other reaction medium and consists solelyof monomers, resultant polymers, land catalyst and regulator, if any. Animportant advantage of the invention is that such `a rnasspolymerization can be eifected to produce 4a clear terpolymer in asituation in which it is impossible to use the gradual monomer additiontechnique discussed above.

lf desired, the interpolymers of the present invention can be made bythe suspension or the emulsion polymerization techniques. For suspensionpolymerization a reaction rnedium such las water is used together with asmall amount of suspending agent, for example tricalcium phosphate,carboxymethylcellulose, etc., to give a suspension of particles ofini-tial monomeric mixture, which particles are not of such small sizeas to result in ya permanently stable latex. Where the particles are ofquite large size, this type of polymerization is often called pearpolymerization. To effect emulsion polymerization, sucient amount ofemulsi-fying agent, for example a water-soluble salt of a sulfonatedlong chain alkyl aromatic compound, a surface active condensationproduct of ethylene oxide with long chain aliphatic alcohols ormercaptans, etc., is employed along with vigorous agitation whereby anemulsion of the reactants in water is formed and the product is obtainedin the form of a latex. The latex can lthen be coagulated ,if desired byknown methods and the polymer separated from the Water. For someapplications the llatex can be employed directly as for example forforming a lm, and the resulting ilm after evaporation of the water willbe clear when the polymers are `made in accordance with the presentinvention. The emulsion technique has certain I'advantages particularlyin that a very high degree conversion of the monomers is obtained withconsiderable rapidity, since the heat of reaction i-s easily carried offby indirect heat exchange with `the reaction mixture which contains aconsiderable proportion of water. Such polymerizations are ofteneffected with redox-type catalyst systems at moderate temperatures ofsay 60 C. on down to 0 C. and below.

The polymers of the present invention can also be made in the presenceof an added organic solvent. It should be recognized however that thepresence of such a solvent ordinarily results in a polymer of lowermolecular weight than that obtained in the absence of the solvent.

Conventional recipes and procedures for eecting mass, solvent,suspension and emulsion polymerizations are so well-known to thoseskilled in the art, thatV they need not be lfurther detailed here.

From the foregoing, -it will ibe apparent that the term, monomericmixture, as used in the claim-s refers only to the polymerizablemonomer-ic materials used in the process, and that -additionallysolvents, aqueous reaction media, catalysts, etc., can be present or notin the reaction mixture as may be desired in any particular case. Inother words, in the claims monomeric mixture is not necessarilysynonymous with reaction mixture.

Polymerization can be effected by any of the wellknown free radicalmechanisms. The polymerization is initiated and carried on by virtue offree radicals, which can be derived from the monomers themselves onsimple heating of the monomeric mixture to a suitable temperature, orcan be derived from added free-radical-supplying catalysts, especiallythe per compounds and the azo compounds, or can be derived byultraviolet or other irradiation of the reaction mixture with or withoutthe presence of photosensitizers, e.g., organic disuliides. The examplesset forth hereinafter describe thermal polymerizations in which thepolymerization reaction was initiated and maintained merely by heatingthe monomeric mixture in the absence of any added catalyst.V In manyinstances it will be desired to add a suitable polymerization catalyst,in which case suiiicient catalyst is employed to give a desired reactionrate. Suitable catalysts are of the free-radical-promoting type,principal `among which are peroxide-type polymerization catalysts, andazo-type polymerization catalysts. Those skilled inthe art are now`fully familiar with Ia large number of peroxide-type polymerizationcatalysts and a suitable one can readily be `chosen by simple trial.Suchcatalysts can be inorganic or organic, the latter having the generalformula: ROOR", wherein R' is an organic radical and R is an organicradical or hydrogen. These compounds are broadlyl termed peroxides, andin a more specific sense are Vhydroperoxides when R is hydrogen. R andR" can be hydrocarbon radicals or organic radicals substituted withk agreat variety of substituents. By way of example, suitable peroxide-typecatalysts include benzoyl peroxide, ditertiary butyl peroxide, tertiarybutyl hydroperoxide, diacetyl peroxide, diethyl peroxycarbonate,Z-phenyl propane-Z-hydroperoxide (known also as cumene hydroperoxide)among the organic peroxides; hydrogen peroxide, potassium persulfate,perborates and other per compounds among the inorganic peroxides. Thelazo-type polymerization catalysts are also well-known to those skilledin the artt. These are characterized by the presence in the molecule ofthe group -N=N- bonded to one or two organic radicals, preferably atleast one ofthe bonds being to ya tertiary carbon atom. By way ofexample of suitable azo-type catalysts can be mentioned a,aazodiisobutyronitrile, p-bromobenzenediazonium fluoborate,N-nitroso-p-bromoacetanilide, azomethane, phenyldiazonium halides,diazoaminobenzene, p-bromobenzenediazonium hydroxide,p-tolyldiazoaminobenzene. 'I'he peroxy-type or azo-type polymerizationcatalyst is used in small but catalytic amounts, which are generally notin excess of one per cent by weight based upon the monomeric material. Asuitable quantity is often in the range of 0.05 to 0.5 percent byweight.

Photopolymerization is another suitable procedure for carrying out thepresent invention. This is ordinarily accomplished by irradiating thereaction mixture with ultraviolet light. Any suitable source of light isemployed having eiective amounts of light with wave lengths of 2,000 to4,000 Angstrom units. The vessel in which the Suitable glasses areavailable commercially and include borosilicate (Pyrex), V5/cor, andsoft glass. Alternatively, the source of light can be placed directlyover the surface of the monomer in a container or can Ibe placed withinthe reaction mixture itself. In some instances it is helpful to add amaterial that can be termed a photosensitizer, i.e., a material whichincreases the rate of pho-topolymerization, for example organic disuldesas described in U.S. Patent No. 2,460,105.

Choice of a suitable temperature for a given polymerization will readilybe made by those skilled in the art having been given the benefit of thepresent disclosure. In general, suitable temperatures'will be foundwithin the range of 0 C. to 200 C., although temperatures outside thisrange are not beyond the scope of the invention in its broadest aspects.The time required for complete polymerization will depend not only uponthe temperature but also upon the catalyst if any is employed, theability of the system to remove heat of polymerization, and theparticular monomers employed. The examples set forth hereinafter givesome illustrative information as to reaction times for particularpolymerizations.

'Ihe term triangular coordinate graph as used herein is well understood.The accompanying figures are examples of such graphs and the use ofsame. However, for the sake of completeness the following statement canbe made concerning the character of such triangular graphs. The graphisan equilateral triangle, divided oi by three series of parallel lineseach series being parallel to one side of the triangle. The distancebetween an apex of the triangle and the side opposite that apexrepresents variations in percentages of the component designated by thatapex varying from percent to 0 percent in equal ncrements running fromthe apex to the opposite side of the triangle. For example, if thedistance between the apex and the side of the triangle opposite the apexis divided into 100 equal parts by lines passing across the triangle andparallel to said side, each line represents l percent of the componentfor which that apex is designated. Thus, any point within `the trianglerepresents a single three-component composition, the indicatedpercentages of the three components totaling 100 percent.

As an aid in the choice of suitable proportions of monomers forpolymerization in accordance with the invention the following data onreactivity ratios of certain monomer pairs are presented by way ofexample. The values given are considered the best ones represented inthe literature or otherwise known, (see Copolymers, by Alfrey, Bohrerand Mark, Interscience Publishers, Inc., 1952, pp. 32-43). In manyinstances an attempt is made to set forth an approximate order ofaccuracy. These latter figures, expressed as plus or minus certainvalues, should not however be given too-much credence since suchattempts to evaluate possible errors are dependent to a considerableextent on subjective evaluation of the data. Most of the values forreactivity ratios given are for moderate temperatures, say between aboutroom temperature (20 C.) and 100 C. Of course, the value of thereactivity ratios for a monomer pair is a function of temperature butthe variation inreactivity-ratios with temperature is quite small and isof little importance unless the polymerization is to be carried out attemperatures considerably removed from those mentioned. Likewise, thereactivity ratios Igiven are for atmospheric or autogenous pressure.Only if the polymerization pressure is to be quite considerablyincreased will there be an important change in the value of thereactivity ratios. It may also be pointed out that in the case of highlywatersoluble monomers the reactivity ratio values may be shiftedsomewhat from those given, when polymerization is effected in an aqueoussystem. Those skilled in the art, having been given the benefit of thepresent disclosure, will ybe able to evaluate the eiect, if any, ofreaction conditions on the values given herein and determine the extentof such effect. Similarly, those skilled in the art can determine bywell-known procedures the correct reactivity ratios for monomer pairsnot specically set forth in the following tabulation, which tabulationis given by way of example of some but not all of the monomers that arethe subject matter of the present invention.

In the following tabulation styrene is considered as M1 and the othermonomers in each instance are considered as M2. Substitution of thevalues for r1 and r2 in the equation given above for the binarypolymerization azeotrope composition permits an immediate determinationof the proper location for the two points to be placed on the triangularcordinate graph, between which points is drawn the line of clearterpolymers.

Where M1 is to be vinyltoluene or Vinylxylene, the same reactivity'ratios are used, on the assumption that the reactivity ratios for suchsystems do not diier essentially for the purposes of this invention fromthe reactivity ratios of the corresponding systems wherein styrene isM1. This assumes that the introduction of one or two methyl groups intothe aromatic nucleus of styrene does not greatly alter the polarity andsteric properties of the vinyl double bond. Likewise, when an alkylmethacrylate other than methyl methacrylate is to be used, thereactivity ratios are assumed not to differ essentially for the purposesof this invention from the above reactivity ratios involving methylmethacrylate. This assumes that a moderate increase in the chain lengthof the alkyl group in the alkyl methacrylates over the single carbonatom in the methyl group of methyl methacrylate, or a branching of thechain if such is present, does not greatly alter the polarity and stericproperties of the vinyl double bond. Similar assumptions are made withrespect to the various dialkyl fumarates as a group, with respect to thevarious monoalkyl fumarates as a group, and with respect to the variousmonoalkyl maleates as a group. Thus, although the reactivity ratios forstyrene/ dimethyl fumarate and for styrene/diethyl fumarate appear todiffer considerably from each other, the values of the binary azeotropecompositions for these two systems calculated from said dif ferentreactivity ratios, given in the table above, differ from each other byonly two percentage points. Anyone skilled in the art, desiring greaterprecision, can use wellknown standard procedures to determine thereactivity ratios for a given binary system not previously reported inthe art. With monomers having fairly long chain alkyl groups, thereactivity ratios tend to differ considerably from those for thecorresponding methyl monomer and hence should be individuallydetermined. Whenever weight percent rather than mole percent is desiredas a matter of convenience, mole percentages of the binary azeotropecompositions are easily converted to weight percent by use of themolecular weights of the particular M1 and M2. In the case of dialkylfumarates, alkyl methacrylates, monoalkyl fumarates, and monoalkylmaleates, any of which can be copolymerized with acrylonitrile and anyone of the monomers styrene, vinyltoluene, and vinylxylene in thepractice of this invention, special preference is given to the loweralkyl groups. Alkyl groups containing from 1 to 4 carbon atoms areparticularly valuable, viz., methyl, ethyl, n-propyl, iso-propyl,n-butyl, iso-butyl, sec-butyl, tert-butyl. However, the invention isalso applicable to the alkyl compounds mentioned, that contain alkylgroups of up to 8 carbon atoms per alkyl group and even higher. In thecase of dialkyl fumarates, there are included those dialkyl fumarateswherein both alkyl groups are the same and those dialkyl fumarateswherein two dierent alkyl groups are present in the molecule. 1

The following examples illustrate some methods for practicing 'thepresent invention with respect to certain ternary mixtures of monomers.The 'general applicability of the invention, and advantages thereof, areshown in these examples. It Vwill be appreciated that variations can bemade in the particular choice of monomers, lproportions, and methods ofpolymerization in accordance with the general teachings of the presentspecication, and the examples are not to be taken as coextensive withthe invention in its broadest aspects.

EXAMPLE I Styrene (M1) Diethyl fumarate (M2) T1=0.30

[Magus-1 -0.92 [Ma-a30- 1- 0.70-

1.3 [M2] -I- [M2] :100:2.3 [M2] [M2] :43.4 mole percent diethyl fumarate[M1]:5 6.6 mole percent styrene Molecular weight of diethylfumarate:l72.2 Molecular weight of styrene: 104.1

0434 172.2: 74.8 grams diethyl fumarate 0566 104.1: 58.8 grams styrene133.6 grams mixture (74.8 133.6:5 6 weight percent diethyl fumarate(58.8X l00)/l33.6:44 weight percent styrene The foregoing calculationsgive the compositions of the styrene/ diethyl fumarate binarypolymerization azeotrope as 44 -weight percent styrene, 56 weightpercent diethyl fumarate.

By the same procedure, the binary polymerization azeotrope forstyrene/acrylonitrile was calculated to be 77 weight percent styrene, 23weight percent acrylonitrile, using slightly diiferent reactivity ratiovalues than in the examples following.

A series of monomeric mixtures was made up, each mixture being preparedby admixture of the individual pure monomers in a Pyrex test tube mm.long and having an internal diameter within the approximate range of 14to 18 mm., usually about 16 mm. Each test tube containing the particularmonomeric mixture was ilushed -with nitrogen in order to remove any airpresent in the gas space above the liquid, and the test tube was thensealed off at the top by heating the tube under nitrogen and pulling itout in the ame to seal the tube completely. Each particular monomermixture was prepared and polymerized in duplicate.

After the various tubes containing the monomeric mixtures had beenprepared, they were placed in a 90 C. constant temperature bath, andheld there for 24 hours. At the end of that period they were moved to a120 C. constant temperature bath and held there for 24 hours. At the endof this second 24-hour period the tubes were removed and placed in anoven maintained at C., and held therein for 8 hours.

The various monomeric compositions are set forth in Al l -detail inTable I. Table I designates each different mixture by sample number.Sample No. l is the binary styrene/acrylonitrile azeotrope composition.Sample No. 6 is the binary styrene/ diethyl fumarate azeotropecomposition. Samples 2, 3, 4, and have compositions which fall on astraight line connecting the two binary azeotrope compositions,designated Samples Nos. l and 6, when plotted on ltriangularcoordinates. See FIGURE I.

Samples 7 to 20, inclusive, were prepared with compositions which variedso that several series of two or three different compositions runningalong constant diethyl fumarate composition lines and cutting across theline joining the two binary azeotropes could be examined.

At the end of the polymerization cycle described above, all the polymersformed in the sealed tubes were carefully examined visually by the sameobserver, looking through the diameter of the cylindrical body ofpolymer obtained by breaking and removing the glass tube; this cylinderof polymer conformed to the internal shape and size of the glass tube.These visual observations were checked by other observers. It wasdetermined that the'clarity noted TABLE I l2 content of the monomericmixture, but consistently ran slightly low, which the literature statesis the uniform experience-in nitrogen determinations on polymers.

The alcohol solubles content of many of the polymers was determined,using the following standard procedure:

A 0.3 gram-sample of polymer is dissolved in 20 ml. acetone (or othersuitable solvent), then the polymer is precipitated by adding 250 ml.absolute ethanol to the solution; the precipitate is coagulated,filtered od, dried and weighed. The average of two determinations isgiven. The alcohol solubles content (ASC) gives an approximate measureofthe extent of conversion. The material soluble in alcohol isprincipally monomer; only very low molecular weight polymers, e.g.,dimers and trimers, are soluble in alcohol. Thus, 10U-ASC approximatesthe percentage conversion.

'Ihe specific viscosity was determined on the total polymer, and on theundissolved residue from the alcohol solubles test. The specificviscosity determinations were made on a 0.1 weight percent solution ofpolymer in dimethylformamide.

Styrene/Acrjylonitrile/Diethyl Fumarate Terpolymers Appearance AlcoholSpecific Viscosity Composition, Percent Solubles Sample No. Wt. PercentAN* n Content,

DEF/NIS Polymer Total Alcohol Clarity Color Percent Polym. InsolubleResidue Colorless Colorless DEF =Diethyl umarate. AN=Acrylonitrile.

S Styrene.

S1. =Slightly.

V. Sl. =Very slightly. Y =Calculated from nitrogen analysis.

for polymer samples is not significantly aected by variation'in polymercylinder diameter within the range of Vabout 14 to 18 millimeters. It isto be understood that where clarity of polymers Vis discussed herein,reference is made to the appearance on looking through acylindri- Vcalbody of the polymer having a diameter withinV the approximate range ofl4 .to 18 millimeters. The following words were adopted for describingthe clarity of polymers.

C-Clear-essentially crystal clear H-Hazy-some cloudiness but slightT-Turbid-moderately cloudy O-Opaque-dense cloudiness-similar to milkglass in appearance Clear means relatively free from gross amounts ofhaze but allows the presence of slight haze to be detected with closeexamination in strong light. Specic notation that a sample was crystalclear means not only that no haze was apparent to the observer, but alsothat the sample showed a sparkling appearance as found in high qualitycrystal glassware.

Several of the polymer products were analyzed for nitrogen and theacrylonitrile content of the polymer calculated. -In each instanceit wasclose to the acrylonitrile Referring now to lFIG. ll of the drawings,the clarity data given in Table I have been designated alongside each ofthe corresponding ternary monomeric mixture composition indicated by apoint on a triangular coordinate plot. The Various numerals on FIG. Ilocated adjacent the respective points refer to the sample number inTable I. All of the points marked C were rated as clear, and of theseall were crystal clear with the exception of points 11 and 12, each ofwhich had a slight haze but not sufficient to consider them other thanessentially clear or to bring them from the clear rating into the hazyrating.

Examination of FIG. I immediately shows that terpolymers prepared frommonomeric mixtures having compositions lying on the line joining the twobinary azeotrope compositions were clear, as were terpolymers within thearea lying along said line. However, going appreciably beyond 5 percenton each side of the line the terpolymers become non-clear. Thus, points7 and l0 were hazy and point 9 was opaque. It is interesting to notethat points 7 and l0 below the line are about 10 percent away from theline and yet only hazy, whereas point 9 above the line s about 7 percentaway from the line and yet is opaque. Such behavior is consistent withmost physical phenomena which seldom exhibit perfect regularity. The

data Vin the .present example demonstrate that .terpolymers made fromternary monomeric mixtures whose .composition is taken from along th:line and from a significant area lying on each side of the line areclear, and also that polymers falling within the area within percent ofeach side ofthe line consitute a new group of terpolymers having ltheextremely important property 4of clarity.

Another interesting thing to note is that by the practice of the presentinvention terpolymers of minimum color ordinarily result. Thus, polymers7 and 10 of those tested, farthest away from the line were yellow, whilethe color decreased as the line was approached. All those polymers lyingbelow the line had at least a trace of yellow color ibut the colorintensity decreased as the line was approached. Those above the line hadno color, other than point 9 which was white and opaque.

ln FIG. lI the dashed lines drawn parallel to the line joining the twobinary azeotrope compositions are 5 percent on each side of the line,i.e., each is a distance from the line equal to 5 percentage points ofcomposition as determined by dividing the distance between an apex andthe center of the opposite side of the triangle into 100 equalequidistant parts.

EXAMPLE 2 This example presents data on the ternary systemstyrene/acrylonitrile/methyl vinyl ketone.

By the procedures used in Example 1, the composition of the Ibinarypolymerization azeotrope styrene/methyl vinyl ketone was calculated,taking styrene as M1 and methyl vinyl ketone as M2. The reactivityratios used were r1=0.29 and 11220.35. The binary polymerizationazeotrope composition was determined to be 42 weight percent methylvinyl ketone, 58 weight percent styrene.

The binary polymerization azeotrope composition forstyrene/acrylonitrile Iwas taken as 76 weight percent styrene, 24 weightpercent acrylonitrile.

Samples containing varying proportions of the monomers were prepared andpolymerized and observations made on the polymers in the mannerdescribed in Example l. However, the polymerization cycle was 29 hoursyat 90 C., 20 hours at 120 C., and finally 8 hours at 180 C. The dataare listed in Table II and plotted in FIG. 1T of the drawings.

TABLE II thereof, and examples have been given of suitable proportionsand conditions, it Will be appreciated that vvaria- Vtions from thedetails ygiven `herein can be effected without departing from theinvention. When desired, the terpolymers of the present -invention canbe -blended with other polymers, plasticizers, solvents, fillers,pigments, dyes, stabilizers, and the like, in accordance .with theparticular use intended.

We claim:

l. A clear terpolymer prepared by free-radical initiated batchpolymerization to a conversion of at least 20 weight percent of amonomeric mixture consisting of (a) a monomer selected from the -groupconsisting of styrene, vinyltoluene and vinylxylene, (b) acrylonitrile,and (c) methyl vinyl ketone, the proportions of the three monomers insaid monomeric mixture being limited to those in the area of mixturesthat produce clear terpolymers, said area encompassing the line joiningthe polymerization azeotrope composition of the particular (a) andacrylonitrile on the one hand and the particular (a) and methyl vinylketone on the other hand as plotted on an equilateral triangularcoordinate graph.

`2. A clear terpolymer prepared by free-radical initiated batch masspolymerization to a conversion of at least 20 weight percent of amonomeric mixture consisting of (a) a monomer selected -from the groupconsisting of styrene, vinyltoluene and vinylxylene, (b) acrylonitrile,and (c) methyl vinyl ketone, the proportions of the three monomers insaid monomeric mixture being limited to those in the area of mixturesthat produce clear terpolymers, said area encompassing the line joiningthe polymerization azeotrope composition of the particular (a) andacrylonitrile on the one hand the particular (a) and methyl vinyl ketoneon the other hand as plotted on an equilateral triangular coordinategraph.

3. A clear terpolymer prepared by free-radical initiated batchpolymerization to a conversion `oi at least 20 Weight percent of amonomeric mixture consisting of (a) styrene, (b) acrylonitrile, and (c)methyl Vinyl ketone, the proportions of the three monomers in saidmonomeric mixture being limited to those in the area of mixtures thatproduce clear terpolymers, said area encompassing the line joining thepolymerization azeotrope composition of styrene and acrylonitrile on theone hand and Styrene/Acrylontrle/Methyl Vinyl Ketone TerpolymersComposition, Wt. Percent S/AN/MVK Appearance Sample No.

Color Alcohol Solubles Content, Wt. percent Specic Viscosity-TotalPolymer Colorless .-..do

Colorless-..

S=Styrene.

AN=Acrylouit1ile.

MVK=Methyl vinyl ketone.

As in the other example, the terpolymers prepared from monomericmixtures whose compositions are on the line joining the two binaryazeotrope compositions, are clear and colorless. -Points 5 and 6, whichare more than 5 percent away from the line in the direction ofincreasing styrene content, are respectively turbid and white, andopaque and white. Points 7, 8 and 9, which are on the opposite side ofthe line `and more than 5 percent away from the line, were all yellow,points 7 and 8 being hazy and point 9 turbid.

While the invention has been described herein with styrene and methylvinyl ketone on the other hand as plotted on an equilateral triangularcoordinate graph.

4. A polymerization process which comprises forming a 3-componentmonomeric mixture consisting of (a) a monomer selected from the groupconsisting of styrene, vinyltoluene and vinylxylene, (b) acrylonitrile,and (c) methyl vinyl ketone, the proportions of the three monomers insaid monomeric mixture being limited to those in the area of mixturesthat produce clear terpolymers, said area encompassing the line joiningthe polymerization azeotrope composition of the particular (a) andparticular reference to various preferred embodiments acrylonitrile onthe one hand and the particular (a) and 15 16 methyl vinyl ketone'on theother hand as plotted on an merio mixtureconsists of (a) styrene, (b)acryloitrile equilateral triangular coordinate graph, and subjecting aand (c) methyl vinyl ketone.

batch of said monomeric mixture to free-radical initiatedbateh'polymerization forming an essentially clear, homo- ReferencesCited in the l 0f this patent geneous, high molecular weight ter-polymerin yan amount 5 UNITED STATES PATENTS of at least 20 weight percent ofsaid monomeric mixture. Y

-T 2,654,721 Lytton Oct. 6, 1953 5. A process according to clalm 4wherem said polym 27,759,910 Milne et al "Y" Aug 21, 1956 erization selected in mass.

6. A process according to claim 4 wherein said mono- 2829125 Slocombe etal Apr' 1 1958

1. A CLEAR TERPOLYMER PREPARED BY FREE-RADICAL INITIATED BATCHPOLYMERIZATION TO A CONVERSION OF AT LEAST 20 WEIGHT PERCENT OF AMONOMERIC MIXTURE CONSISTING OF (A) A MONOMER SELECTED FROM THE GROUPCONSISTING OF STYRENE, VINYLTOLUENE AND VINYLXYLENE, (B) ACRYLONITRILE,AND (C) METHYL VINYL KETONE, THE PROPORTIONS OF THE THREE MONOMERS INSAID MONOMERIC MIXTURE BEING LIMITED TO THOSE IN THE AREA OF MIXTURESTHAT PRODUCE CLEAR TERPOLYMERS, SAID AREA ENCOMPASSING THE LINE JOININGTHE POLYMIZATION AZEOTROPE COMPOSITION OF THE PARTICULAR (A) ANDACRYLONITRILE ON THE ONE HAND AND THE PARTICULAR (A) AND METHYL VINYLKETONE ON THE OTHER HAND AS PLOTTED ON AN EQUILATERAL TRIANGULARCOORDINATE GRAPH.